1. Field of the Invention
The present invention relates generally to devices used for hoisting and binding heavy loads and, particularly, to such devices having indicia for determining certain stressing thereof.
2. Description of the Related Art
Devices for hoisting heavy loads, such as with a crane, are well known. A variety of different designs have been developed to meet the requirements of particular applications. For example, such devices include hooks, shackles, links, rings, and the like.
Each of these devices are generally designed to have certain maximum load or stress limits. Sometimes, these devices are subjected to loads and stresses which exceed those maximum limits. Although such excessive stresses may not cause the overloaded device to fracture, it may cause the device to deform. Due to such deformation, the maximum load which the device can subsequently withstand without fracture may have been drastically reduced. Thus, it is extremely important that such deformation be detected before serious damages or injuries result therefrom.
Unfortunately, such deformation may only be signalled by relatively minor variations in the outward appearance of an overstressed device. As a result, the fact that a device has been damaged may not be readily apparent visually. An attempt to solve this problem was provided in U.S. Pat. No. 5,103,755, issued Apr. 14, 1992 to C. R. Garrett. That patent teaches spacing a pair of markers at a known, fixed distance apart across the throat of a hook. A subsequent deviation from that spacing indicates that the hook has been overstressed and should be replaced. Unfortunately, a user who failed to have a measuring device available at the time the spacing was checked would be provided no greater protection by one of the devices taught by the '755 patent than he would have been provided by a device without the pair of markers.
In addition, some uses of a hoisting device may, for one reason or another, not allow a user to approach the device to inspect it for deformation from overstressing. For example, the device may be used for handling hazardous material or be positioned such that one cannot physically measure the spacing with a scale, etc. Further, it may be desirable in some applications to be able to determine whether a particular load being handled by a hoisting device is within the maximum load designed for that device.
Thus, what is needed is a device which can be inspected for overloading without a measuring instrument, which can be remotely inspected for deformation, and which can be remotely inspected to determine whether a particular load being handled by the device is within design load limits.